Immune stimulatory cytokines can be exploited to treat human ailments including cancer. Amongst cytokines identified for such use, Granulocyte-Macrophage-Colony Stimulating Factor (GM-CSF) has been under much scrutiny since it acts directly on the adaptive immune system by enhancing antigen presentation as well as costimulation1,2. Furthermore, second generation strategies linking innate and adaptive immunity using GM-CSF delivered as a fusion cytokine (fusokine) with other immune stimulatory proteins such as Interleukin-2 (IL-2) and IL-3 have been developed3,4. GM-CSF was first described as a growth factor for granulocyte and macrophage progenitor cells. However, GM-CSF is also an important mediator for inflammatory reactions produced by T lymphocytes, macrophages and mast cells present at sites of inflammation5. GM-CSF is a strong chemoattractant for neutrophils. It enhances microbicidal activity, phagocytotic activity and cytotoxicity of neutrophils and macrophages. An important feature of GM-CSF is that it greatly enhances the state of antigen presentation on dendritic cells, known to be crucial mediators of acquired immunity. The DNA and protein sequences of GM-CSF have been protected under PCT application WO8600639 and the derived patents.
IL-15 is a pleiotropic cytokine that plays an important role in both the innate and adaptive immune system. IL-15 promotes the activation of neutrophils and macrophages, and is critical to dendritic cell function. In addition, IL-15 is essential to the development, homeostasis, function and survival of natural killer (NK) cells, NK T (NKT) cells and CD8+ T cells. Based on these properties, IL-15 has been proposed as a useful cytokine for immunotherapy. It is currently being investigated in settings of immune deficiency, for the in vitro expansion of T and NK cells, as well as an adjuvant for vaccines6. The only stimulatory IL-15 molecule has been described in the form of the cDNA of IL-15 in U.S. Pat. No. 5,552,303.
IL-15 is expressed in several inflammatory disorders, including rheumatoid arthritis, psoriasis, pulmonary inflammatory diseases and diabetes. The beneficial effect of IL-15 neutralisation in autoimmune disease models of psoriasis and diabetes has been proposed in the literature7. IL15 antagonists, such as IL-15 “muteins”, Fc derivatives, or antibodies directed against IL-15 or IL-15 Receptor (IL-15R) have been developed for immunosuppression8,9. U.S. Pat. No. 6,013,480 refers to an antagonist of IL-15 encoded by a DNA of IL-15 mutated in Asp56 or Gln156 via addition, substitution, or deletion that still binds to the IL-15 R α-subunit but no longer to the β or γ-subunits thus preventing any signal transduction. U.S. Pat. No. 6,165,466 describes an IL-15 specific monoclonal antibody directed against the epitopes containing Asp56/Gln156 preventing signal transduction via the IL-15 R. This antibody is protected in its humanized form under U.S. Pat. No. 6,177,079.
IL-2 and IL-15 have pivotal roles in the control of the life and death of lymphocytes. Although their heterotrimeric receptors have two receptor subunits in common, these two cytokines have contrasting roles in adaptive immune responses. The unique role of IL-2 is in the elimination of self-reactive T cells to prevent autoimmunity. By contrast, IL-15 is dedicated to the prolonged maintenance of memory T-cell responses to invading pathogens.
Therefore, both cytokines could affect the immune system as complimentary fusion proteins in the development of novel therapies for malignancy and autoimmune diseases, as well as the design of vaccines against infectious diseases10.